linux-kernel - Re: [PATCH 1/1] mtd: spi-nor: improve macronix_quad

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Date:   Wed, 7 Dec 2016 00:46:59 +0100
From:   Marek Vasut <marek.vasut@...il.com>
To:     Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Cyrille Pitchen <cyrille.pitchen@...el.com>
Cc:     boris.brezillon@...e-electrons.com, computersforpeace@...il.com,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        richard@....at
Subject: Re: [PATCH 1/1] mtd: spi-nor: improve macronix_quad_enable()

On 12/07/2016 12:05 AM, Cyrille Pitchen wrote:
> Le 06/12/2016 à 20:01, Marek Vasut a écrit :
>> On 12/06/2016 05:01 PM, Cyrille Pitchen wrote:
>>> The patch checks whether the Quad Enable bit is already set in the Status
>>> Register. If so, the function exits immediately with a successful return
>>> code.
>>
>> Performance optimization I presume ?
> 
> Performance optimization is one benefit but this real purpose of the
> patch is to avoid writing over and over a non-volatile bit at each boot,
> actually each time spi_nor_scan() is called.
> 
> To be honest, I don't know whether internally the SPI memory is clever
> enough not to perform the actual write when it sees the bit value has
> not changed. I wanted to improve the memory lifetime by avoiding the
> update of the bit from software just to be sure :)

Well the bit is in some sort of internal SRAM or silicon register , no?

> Anyway, thanks for your review!

np

>> Acked-by: Marek Vasut <marek.vasut@...il.com>
>>
>>> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@...el.com>
>>> Reviewed-by: Jagan Teki <jagan@...nedev.com>
>>> ---
>>>  drivers/mtd/spi-nor/spi-nor.c | 3 +++
>>>  1 file changed, 3 insertions(+)
>>>
>>> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
>>> index da7cd69d4857..1fd32b991eb7 100644
>>> --- a/drivers/mtd/spi-nor/spi-nor.c
>>> +++ b/drivers/mtd/spi-nor/spi-nor.c
>>> @@ -1216,6 +1216,9 @@ static int macronix_quad_enable(struct spi_nor *nor)
>>>  	val = read_sr(nor);
>>>  	if (val < 0)
>>>  		return val;
>>> +	if (val & SR_QUAD_EN_MX)
>>> +		return 0;
>>> +
>>>  	write_enable(nor);
>>>  
>>>  	write_sr(nor, val | SR_QUAD_EN_MX);
>>>
>>
>>
> 


-- 
Best regards,
Marek Vasut